Father Donald (The Western Heritage) and son Frederick, professors of history at Yale and West Point respectively, have combined their talents to produce a frightening story of close parallels between Great Britain in the 1920s and 1930s and America in the 1990s. After 1918, Britain slashed its armed forces and defined its interests in the context of international organizations and agreements. The result, contend the Kagans, was a foreign policy of ""pseudo-engagement""--rhetoric unaccompanied by the effective use of force--that steadily undermined Britain's credibility. In a series of chapters written in acid, the Kagans argue that the U.S. has set itself up for a similar fall by diminishing its military capacities in pursuit of an ephemeral ""peace dividend"" and by overextending its armed forces in pursuit of poorly defined responsibilities--Iraq, the Balkans, North Korea. The Kagans suggest that the U.S. now stands about where Britain did at the end of the 1920s--somewhere on the bubble: in a position to restore the balance between military power and international responsibility, but facing strong temptations to procrastinate and deny. (It was 1938, the Kagans point out, before the British government faced squarely the consequences of its relative disarmament.) Readers may not agree with the Kagans' analysis of the synergy between military power and national policy, but they will be impressed by the force of their argument and the power of their reasoning. (Oct.)